Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C₂-symmetric building block: a strategy for the synthesis of decanolide natural products

• Bernd Schmidt and
• Oliver Kunz

Beilstein J. Org. Chem. 2013, 9, 2544–2555, doi:10.3762/bjoc.9.289

• ). With borane–dimethylsulfide complex as the reductant and 10 mol % of catalyst, no conversion was observed at −78 °C (Table 3, entry 1), whereas attempted reduction at ambient temperature (Table 3, entry 2) resulted in the formation of a complex mixture, presumably due to competing hydroboration of the

• alkenes. With borane–THF at −50 °C the reduction proceeded to completion, but gave a 1:1 mixture of diastereomers (Table 3, entry 3). With catechol borane at −78 °C conversion was again complete, but the diastereoselectivity was far from being synthetically useful (Table 3, entry 4). Due to these rather

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• strong P1 base polymer-supported BEMP gave the corresponding ether adduct which was then converted to the desired secondary amine 1.64 via direct amidation and borane-mediated reduction. Next an SNAr reaction on 2-fluoropyridine (1.66) followed by oxidation of the benzylic alcohol using immobilised

• developed, initial masking of the acid (1.104) is achieved by silylation with subsequent borane chelate formation. Addition of the amine nucleophile 1.105 under basic conditions then renders the desired product in high yield. The available patent literature however does not comment on regioselectivity

Flow Giese reaction using cyanoborohydride as a radical mediator

• Takahide Fukuyama,
• Takuji Kawamoto,
• Mikako Kobayashi and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2013, 9, 1791–1796, doi:10.3762/bjoc.9.208

• reductive radical addition reaction, better known as the Giese reaction, was historically carried out most by using tributyltin hydride as the radical mediator [8][9]. Recently borane derivatives such as borohydride reagents [10][11][12][13] or NHC-boranes [14][15][16][17][18] can be used in simple radical

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• decyanation step. We planned to synthesize 5 by reaction of the cyanohydrin acetonide 67 with the epoxide electrophile 66 (Figure 8) [67]. The dimethyl derivative of L-malic acid was chemoselectively reduced with borane-dimethylsulfide and sodium borohydride to afford diol 69 (Scheme 18) [68]. The primary

Methylidynetrisphosphonates: Promising C₁ building block for the design of phosphate mimetics

• Vadim D. Romanenko and
• Valery P. Kukhar

Beilstein J. Org. Chem. 2013, 9, 991–1001, doi:10.3762/bjoc.9.114

• reasonable yield, but the 1-allyl-substituted trisphosphonate 12b did not undergo hydroboration with 9-BBN. However, treatment of 12b with borane in THF resulted in conversion to the primary alcohol 34 in good yield (Scheme 16) [26]. A further example of the reactivity of trisphosphonates is provided by a

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

• Huili Liu,
• Kuan Zheng,
• Xiang Lu,
• Xiaoxia Wang and
• Ran Hong

Beilstein J. Org. Chem. 2013, 9, 983–990, doi:10.3762/bjoc.9.113

• delivers iminolactones A. The reduction with borane gives hydroxyamine 13. In this new proposal, the iminolactone A could be unstable and difficult to purify according to Tellitu’s findings [46]. Similar stability of iminolactone is documented in the literature [53][54][55]. Although we have established

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• Vladimir Lamm Xiangcheng Pan Tsuyoshi Taniguchi Dennis P. Curran Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 USA 10.3762/bjoc.9.76 Abstract Acetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3

• -dimethylimidazol-2-ylidene borane. Aldehydes are reduced over 1–24 h at room temperature with 1 equiv of acetic acid and 0.5 equiv of the NHC-borane. Ketone reductions are slower but can be accelerated by using 5 equiv of acetic acid. Aldehydes can be selectively reduced in the presence of ketones. On a small

• scale, products are isolated by evaporation of the reaction mixture and direct chromatography. Keywords: NHC-borane; N-heterocyclic carbene borane; reduction; Introduction Reduction of carbonyl compounds is a common, fundamental chemical transformation. Among the numerous hydride reagents available

A new synthetic protocol for coumarin amino acid

• Xinyi Xu,
• Xiaosong Hu and
• Jiangyun Wang

Beilstein J. Org. Chem. 2013, 9, 254–259, doi:10.3762/bjoc.9.30

• coumarinylacetic acid, which was then reduced to an alcohol by borane-dimethyl sulfide. After the phenolic hydroxy group was protected with a tert-butyl(dimethyl)silyl group, the alcohol was converted into a bromide and was used to alkylate a glycine enolate synthon to afford an imine. All the protecting groups

Synthesis of a derivative of α-D-Glcp(1->2)-D-Galf suitable for further glycosylation and of α-D-Glcp(1->2)-D-Gal, a disaccharide fragment obtained from varianose

• Carla Marino,
• Carlos Lima,
• Karina Mariño and
• Rosa M. de Lederkremer

Beilstein J. Org. Chem. 2012, 8, 2142–2148, doi:10.3762/bjoc.8.241

• -2, C-3), 73.3 (CH2Ph), 72.4 (CH2Ph), 71.1 (C-5’), 69.8 (C-5), 67.8 (C-6’), 62.2 (C-6); Anal. calcd for C61H56O14: C, 72.32; H, 5.57; found: C, 72.39; H, 5.65. 2-O-(2,3,4,6-Tetra-O-benzyl-α-D-glucopyranosyl)-3,5,6-tri-O-benzoyl-α,β-D-galactofuranose (8): To a solution of bis(2-butyl-3-methyl)borane

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• electron-deficient Lewis acid. In the case where molecular hydrogen interacts with a phosphine/borane FLP, this occurs by the formation of a phosphonium/borate ion pair (Scheme 1). For unsaturated substrates, the reaction is better described as an insertion or cycloaddition (see Scheme 2 for a

• ]. Single-crystal X-ray structure of a silver(I) triflate adduct of (PNP)Ir═C(H)Ot-Bu with most H atoms and phosphine substituents (except ipso carbon atoms) omitted for clarity. Heterolytic cleavage of H2 by a phosphine/borane FLP by H2 polarization in the P–B cavity [5][11]. Insertion of carbon dioxide

• into a phosphine/borane FLP [14]. Oxygen-atom extrusion from CO2 by a Ta(V) neopentylidene [27]. Oxygen-atom transfer from acetone at a Zr(IV) imide [28]. Alkyne cycloaddition at a Zr(IV) imide [38]. Nitrile-alkyne cross metathesis at a W(VI) nitride [40][41]. C–H and H–H addition across a zirconium(IV

Synthesis of chiral sulfoximine-based thioureas and their application in asymmetric organocatalysis

• Marcus Frings,
• Isabelle Thomé and
• Carsten Bolm

Beilstein J. Org. Chem. 2012, 8, 1443–1451, doi:10.3762/bjoc.8.164

• this reason, a heterochiral product was prepared by coupling (R)-2 (the mirror image of the previously applied sulfoximine) with N-Boc protected L-leucine to give (RS,SC)-15 (84% yield). Reduction of the two N-acylated sulfoxmines (SS,SC)-14 and (RS,SC)-15 with borane-THF complex led to removal of the

Synthesis of compounds related to the anti-migraine drug eletriptan hydrobromide

• Suri Babu Madasu,
• Nagaji Ambabhai Vekariya,
• M. N. V. D. Hari Kiran,
• Badarinadh Gupta,
• Aminul Islam,
• Paul S. Douglas and
• Korupolu Raghu Babu

Beilstein J. Org. Chem. 2012, 8, 1400–1405, doi:10.3762/bjoc.8.162

• % yield. Synthesis of impurity 5. Reagents and conditions: (i) Acetic anhydride, TEA, DMF, 90–100 °C; (ii) palladium acetate, tri-(o-tolyl)phosphine, K2CO3, triethyl borane in THF (1 M), THF, 64–66 °C; (iii) methanol, K2CO3, methylene chloride, H2O, 5–10 °C and 85% yield. Debromination of 9 to 6. Reagents

Chemo-enzymatic modification of poly-N-acetyllactosamine (LacNAc) oligomers and N,N-diacetyllactosamine (LacDiNAc) based on galactose oxidase treatment

• Christiane E. Kupper,
• Ruben R. Rosencrantz,
• Birgit Henßen,
• Helena Pelantová,
• Stephan Thönes,
• Anna Drozdová,
• Vladimir Křen and
• Lothar Elling

Beilstein J. Org. Chem. 2012, 8, 712–725, doi:10.3762/bjoc.8.80

• excess of picoline–borane complex and two-fold excess of acetic acid in methanol:H2O mixture (approx. 6:1) [72][73][74]. Reaction mixtures were incubated at 60 °C for 19 h. The analysis and small-scale isolation of products 18 and 19 were performed by reversed-phase HPLC using method A and ESI–MS

Reciprocal polyhedra and the Euler relationship: cage hydrocarbons, C_nH_n and closo-boranes [B_xH_x]²⁻

• Michael J. McGlinchey and
• Henning Hopf

Beilstein J. Org. Chem. 2011, 7, 222–233, doi:10.3762/bjoc.7.30

• , 12) are in accord with Euler's equation. Interestingly, the tetrahedron (4 vertices, 6 edges and 4 faces) is its own reciprocal. Boranes, hydrocarbons and inverse polyhedra Closo-borane anions and their carborane analogues adopt polyhedral structures in which each face is triangular [3]; Figure 3

• the borane that has a capping boron linked to six others. We are unaware of any attempted syntheses of this molecule but, as depicted in Scheme 14, suitable disconnections reveal that a C3-bridged ansa-[5]peristylane is an enticing precursor to 15. Highly symmetric inorganic polyhedranes The major

• original concept and propose that other highly symmetrical cage hydrocarbons of the CnHn type might have closo-borane counterparts. Indeed, Lipscomb and Massa have discussed the structures of borane analogues of fullerenes [52][53] and even of nanotubes [54]. In particular, they proposed that C60 (V, E, F

Recent advances in the development of alkyne metathesis catalysts

• Xian Wu and
• Matthias Tamm

Beilstein J. Org. Chem. 2011, 7, 82–93, doi:10.3762/bjoc.7.12

• several phenylalkynes, and yields up to 64% were obtained by application of relatively forcing reaction conditions (10 mol % nitride, 20 mol % borane, 30 mol % phenol, T = 90 °C). Nevertheless, the rate of metathesis is enhanced in comparison with the performance of the borane-free complexes, and these

CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF₃ and BH₃

• Julien Monot,
• Louis Fensterbank,
• Max Malacria,
• Emmanuel Lacôte,
• Steven J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2010, 6, 709–712, doi:10.3762/bjoc.6.82

• -dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC–BF3 complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH3) was readily

• formed in situ according to 1H and 11B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes. Keywords: borane Lewis acid Lewis base complexes; carbene–borane complexes; cyclic (alkyl) (amino) carbenes; N-heterocyclic

• , sulfides, etc.), NHC–borane complexes are highly stable in diverse environments. Complexes such as those shown in Figure 1 are white solids that can often be chromatographed if desired. Many such complexes resist decomplexation, oxidation, and both acidic and basic hydrolysis. Such NHC–boranes are

Synthesis of the fluorescent amino acid rac-(7-hydroxycoumarin-4-yl)ethylglycine

• Manfred Braun and
• Torsten Dittrich

Beilstein J. Org. Chem. 2010, 6, No. 69, doi:10.3762/bjoc.6.69

• acetonedicarboxylate. First, the acid 2 was reduced to the alcohol 3 with borane. The protocol described in the literature [12] was modified, and the reducing agent borane–tetrahydrofuran replaced by the less expensive borane–dimethyl sulfide. This also led to a slight increase in yield (59%). For the planned

• 0 °C. Through the dropping funnel, a 10 M solution of borane–dimethyl sulfide (12 mL, 120 mmol) in THF, diluted with 100 mL of dry THF was added dropwise over 60 min at 0 °C. Stirring was continued at r. t. for 24 h. After cooling to 0 °C, water (10 mL) was cautiously added. The mixture was

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• of the aziridine. They exploited the presence of a β-dicarbonyl functionality in 71 to introduce a phenylseleno function α to the lactam centre (Scheme 20). Then, hydrolysis of the methyl ester followed by decarboxylation and reduction of the lactam with borane gave the selenide diastereoisomers 72

Diastereoselective and enantioselective reduction of tetralin- 1,4-dione

• E. Peter Kündig and
• Alvaro Enriquez-Garcia

Beilstein J. Org. Chem. 2008, 4, No. 37, doi:10.3762/bjoc.4.37

• (yields: 76–98%). Fractional crystallization allowed isolation of the cis-diol and the trans-diol (55% and 66% yield, respectively). Borane was used to cleanly give the mono-reduction product. Highly enantioselective CBS reductions afforded the trans-diol (72% yield, 99% ee) and the mono-reduction product

• borane compared to the reduction detailed above. For the bis reduction, a molar ratio of 2 / BH3 of 0.83 was used. Adjusting the ratio to 2.2 (see experimental part) afforded rac-9 in good yield (Scheme 5). The high yield in mono-reduction is in accord with the expected higher reactivity of the dione 2

A divergent asymmetric approach to aza-spiropyran derivative and (1S,8aR)-1-hydroxyindolizidine

• Jian-Feng Zheng,
• Wen Chen,
• Su-Yu Huang,
• Jian-Liang Ye and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2007, 3, No. 41, doi:10.1186/1860-5397-3-41

• more conveniently, N,O-acetal 5a, was converted to lactam 6a under standard reductive dehydroxylation conditions in 78% or 77% yield. Reduction of lactam 6a with borane-dimethylsulfide provided pyrrolidine 8 in 95% yield. Compound 8 was then converted to 1-hydroxyindolizidine ent-3 via a four-step

• the same conditions, N,O-acetal 5a was converted to lactam 6a in 77% yield. It was observed that during the reaction of 5a, 7 was first formed as an intermediate after the addition of Et3SiH and BF3·OEt2, and stirring for 1 hour. Reduction of lactam 6a with borane-dimethylsulfide provided pyrrolidine

Multiple hydride reduction pathways in isoflavonoids

• Auli K. Salakka,
• Tuija H. Jokela and
• Kristiina Wähälä

Beilstein J. Org. Chem. 2006, 2, No. 16, doi:10.1186/1860-5397-2-16

• (Table 3). [16][29][34] Isoflavanones are reduced by electrophilic hydrides (borane-tetrahydrofuran, bis-tert-butylthioethane borane) diastereoselectively to cis-isoflavan-4-ols, but a large excess of the reducing agent is usually needed [29]. Although it was realized by the early workers that

Hydrogenation of aromatic ketones, aldehydes, and epoxides with hydrogen and Pd(0)EnCat™ 30NP

• Steven V. Ley,
• Angus J. P. Stewart-Liddon,
• David Pears,
• Remedios H. Perni and
• Kevin Treacher

Beilstein J. Org. Chem. 2006, 2, No. 15, doi:10.1186/1860-5397-2-15

• hydrides (NaBH4, LiAlH4) and their derivatives, in addition to borane and substituted boranes, which are the most commonly used. [1][2][3][4] However, from a practical point of view a more attractive approach is to develop a selective heterogeneous catalyst that is efficient for this transformation. From